A roll press includes two interacting press rolls which form a nip between them. The rolls are generally arranged in a vat into which the stock suspension, such as a pulp suspension, is introduced. The rolls are designed so that their shell surfaces allow water to pass through, thereby dewatering the suspension due to the fact that the liquid is pressed in through these surfaces by a positive pressure. In the nip between the press rolls, final dewatering takes place in order to provide the desired dry-solids content of the stock. The shell surfaces of the press rolls consist of perforated plating attached to the roll frameworks. In order to obtain sufficient capacity, the total area of the open holes in the plating must be large, but the holes also must be kept small to prevent fibers from following along with the liquid as it passes through the holes. To accomplish this when processing short fibers, the press roll is provided with a wire cloth outside the perforated shell plating. Press rolls clad with a wire cloth have proven to be especially advantageous for mechanical pulp, which contains large amounts of short fibers; i.e., fine stock. Compared with conventional plating, the wire cloth permits smaller amounts of fine stock to pass through.
The rolls partially submersed in the vat are arranged to rotate on two parallel shafts, such that the vat surrounds at least the lower half of the rolls. The stock suspension is introduced into the space between the rolls and the vat. This space is sealed off from the environment in such a way that a positive pressure can be maintained in the vat in order to facilitate dewatering. Seals are herewith provided at the upper edge of the vat, and they seal against the ends of the rolls and also along the shell surfaces of the rolls. Such seals are described, for example, in Swedish Patent No. 503,010. Between the rolls, the nip itself and the pulp web that passes continuously through it serve as a seal against the environment. Doctor blades are also provided downstream of the nip to remove the dewatered pulp web from the rolls. Thereafter, the pulp is carried away by means of a conveyor to the next step in the process.
Experience has shown that the type of seal used in the past, which extends longitudinally along the shell surface of the roll, wears out too rapidly. This seal, which consists of a single piece of bent sheet steel, is also disadvantageous because if one increases the wear strength of the sheet steel, the stiffness of they spring changes. In addition, the sheet steel becomes more difficult to bend when it in made harder in order to reduce wear. In the event that the seal breaks down, not only must operation be stopped but the machine wire may be cut off and this, in turn, can ruin large amounts of pulp. The purpose of the present invention is to solve the aforesaid problems.